Many processes and devices have been used in the field of pressure sensing. Pressure sensors are generally used and deployed wherever a need for monitoring and responding to pressure changes is necessary. Pressure sensors are commonly used in a variety of automotive, aerospace, commercial, industrial, and consumer applications.
The operational environments in which pressure sensors are required to operate in these applications with high accuracy and repeatability can be very demanding. For example, extreme thermal conditions including thermal shocks in ranges from 160 C to −55 C, exposure to harsh and/or conductive media, withstand high overpressure (proof pressure) cycling without change in calibration and survive high peak (burst) pressures to protect system from potentially catastrophic leaks.
In the case of a pressure sensor that relies upon the use of a pressure transducer (or sense element) including piezoresistive silicon on an etched silicon diaphragm, a most cost effective solution for operating in such environments is to use so called “back-side” sensing. With this arrangement the only parts of sensor which are exposed to the media are the electrically isolated cavity side of the pressure transducer, the adhesive used to bond the transducer die to a substrate and finally the substrate itself.
FIGS. 1-4 illustrate example prior art pressure sensor apparatus configurations. FIG. 1 illustrates a cross sectional view of a prior art direct chip-on-board mounted pressure sensor apparatus 100. The configuration illustrated in FIG. 1 generally includes a pressure transducer/die 102 that is attached to a printed circuit board (PCB) substrate 106 with the assistance of a die-attach adhesive 104. A plurality of bond wires 110 are also depicted in the configuration illustrated in FIG. 1. The bottom portion of the pressure sensor apparatus 100 includes a housing 108. A top cover 105 or protective portion is also included. The configuration depicted in FIG. 1 is generally presented for background and edification purposes only and is not considered a limiting feature of the disclosed embodiments.
FIG. 2 illustrates a side sectional view of another prior art sensor apparatus 200. FIG. 3 illustrates a portion of a prior art sensor system 400 in which the sensor apparatus 200 can be implemented, while FIG. 4 illustrates a larger view of the system 400 together with the prior art pressure sensor apparatus 200. FIGS. 2-4 are illustrated as a contrast to the improved sensor apparatus 500, which is described in greater detail herein. Note that in FIGS. 2-4, identical or similar parts or elements are generally indicated by identical reference numerals. The prior art sensor apparatus generally includes a PCB (Printed Circuit Board) 201 in association with one or more bond wires 204, 255, and 257. An electronic component 212 can communicate with the PCB 201 via bond wires 255 and 257. Similarly, an electronic component 243 can communicate with the PCB 201 via the bond wire 204.
An adhesive or glue 209 is generally utilized to maintain a contact clip 202 with respect to the PCB 201. A glue 208 can also be utilized to maintain the component 243 to the carrier 204. Additionally, a cover or housing 203 surrounds the components 243 and 212. An adhesive may be utilized to maintain the component 212 to the PCB 201. The pressure sensor apparatus 200 includes the carrier 204 in which a port 251 is disposed and configured within the carrier 204. As shown in FIG. 3, the carrier 204 can be configured from a rigid material 207, which is preferably a metal such as aluminum in order to ensure that the carrier 204 is rigid. A section 402 as depicted in FIG. 4 generally constitutes a fitting while the area 404 can include threads. Areas 207 and 402 together can constitutes a valve such as a Schrader valve. The port 251 depicted in the prior art configuration of FIG. 204 extends toward and into an area 261 of the carrier 204. The area 261 thus extends through the cross section of PCB 201, offering a limited area for component attachment.
One of the problems with the prior art configurations illustrated in FIGS. 1-4 is that such designs need to operate reliably under the conditions described earlier and with the use of attach materials which have high strength and chemical resistance. The rigid mounting of a stress sensitive die (e.g., pressure transducer), for example, onto a PCB where there is a large mismatch in thermal expansion coefficient between the die and the PCB can introduce high levels of package stress, which can result in output errors, non-repeatability and potentially, mechanical damage.
Pressure sensor designs are known, which include the use of a Si piezoresistive die mounted to a metal carrier via an adhesive or epoxy. Such metal carriers not only serve as a substrate or pedestal, but when assembled in the final product design also serve to mate, for example, with a Schrader valve in an automotive HVAC system. These metal carriers are typically made of aluminum, which is known to possess a high affinity for oxygen and quickly forms oxides when exposed to the open environment and adversely affects adhesion. Other times, a plating or coating must be implemented to allow adhesion between the silicon pressure die and the metal carrier. Common platings in the field use chromium and this material is being eliminated from use in a number of countries, including those in Europe. Removing this material from the plating does not allow for a strong bond between the sense die and the carrier. Therefore, in order to overcome this problem, it is believed that a solution lies in the implementation of an improved pressure sensor method and system, which is disclosed in greater detail herein.